Process of separation of air into its elements



1386- 1959 J; F. GRUNBERG PROCESS OF SEPARATION OF AIR INTO ITS ELEMENTSFiled. Sept. 27, 1956 17zue/2ZZ/ JYCQUES FT GRUIVBFRG United States P nPROCESS OF SEPARATION OF AIR' INTO ITS ELEMENTS Jacques F. Grunberg,Outremont, Quebec, Canada, as-

signor to LAir Liquide, Societe Anonyme pour lEtude et l'Exploitationdes Procedes Georges Claude, Paris, France, a body politic and corporateApplication September 27, 1956, Serial No. 612,441

7 Claims. (CI. 62-25) section of the unit, or a part of the gaseousnitrogen.

obtained in the rectification high pressure column of a two-columnrectification process.

It is characteristic of the present invention that the: low pressurestage used for the rectification is appre ciably higher than atmosphericpressure and that at least: one of the product gases delivered by thelow pressure column is expanded, at least in part, with production of:'

external work.

As the flow of expanded gas can be important (for ex-- ample, the totalamount of nitrogen product can be ex+' panded), the refrigerationproduced is considerable, even for a relatively small expansion ratio,and it is possible: to produce all the refrigeration necessary for theoperation of the unit in expanding nitrogen from a relativelylowpressure, for example, from 2 kg./cm. absolute pressure down to apressure close to the atmospheric pres-- sure.

The expansion of the product gas can be carried out: in a turbine, thistype of machine having a'high efficiency for low expansion ratios, andbeing particularly con-' venient when the actual volume of gases to beexpanded. is relatively considerable. In the case of small units,. wheregenerally reciprocating engines are used for the: expansion of highpressure air, the reciprocating engine: can be replaced by a turbineexpanding low pressure nitrogen, as per the invention. The turbine willgive greater running security, will be less cumbersome, and. cheaperthan the conventional reciprocating expansion. engine.

It should be also noticed that, due to the low intake and dischargepressures of the turbine, smaller gas leaks will be experienced than onturbines running at higher" pressures.

The gas, which leaves the top of the low pressure column at a very lowtemperature, must first be reheated before expansion in order toincrease the efliciency of' the expansion and avoid a partialliquefaction. In a preferred arrangement of the invention, the gas whichmust be expanded, is first reheated before expansion by heat transferwith a liquid leaving the high pressure column. The liquid is furtherexpanded and delivered to a low pressure column.

Besides, the gas which is expanded in the turbine leavesit too cold tobe sent directly to the heat exchanger sec-- tion destined to cool theair to be treated. In another type of arrangement of the presentinvenion, the expanded gas is reheated as above, by heat transfer with aliquid. leaving the high pressure column and sent to a low pressurecolumn.

It is seen that for the reheating of the gas, before and" afterexpansion, the liquid coolers can be used. These liquid coolers arestandard on these plants to reduce the: amount of liquid vaporizedthrough the expansion. The" liquid coolers can be used as super heatersfor the gas,. due to the relatively low temperature drop, which resultsfrom the expansion of the gas.

An interesting application of the present invention con-1- cerns theunits where the separation of air produces'v gaseous oxygen underpressure through the vaporization.-

of liquid-oxygen compressed beforehand.

' It is well known that, in order to produce oxygenunder pressure, thecompressed air to be separated is used both for the vaporization of theliquid-oxygen under pressure by heat transfer with the liquid-oxygen,and for the production of refrigeration through expansion with externalwork. Due to the fact that the vaporization of liquidperature of theoxygen, in order to obtain a good efiiciency oxygen under pressurerequires a large amount of heat supplied at a relatively hightemperature, it is necessary in the conventional processes to compressair at a pressure which is appreciably higher than that of the pro-' Yduced oxygen, so that the heat transfer can be carried out.

a If a part of the high pressure air has to be expanded with externalwork in the conventional processes, it is generally necessary to send itto the expansion engine at a temperature which is higher than thevaporization temof the expansion without partial liquefaction in theengine.

The total amount of air which remains available for the vaporization ofthe high pressure oxygen, is then reduced and the air pressureappreciably increased in order t compensate for the reduction of theoutput.

The present invention permits avoidance of the abovementionedinconveniences. Refrigeration is suppliedby expansion with external workof at least one of the product gases collected at one of the lowpressures used for whereas the second fraction is sent after cooling atabout its initial pressure to the rectification section of the plant.-

A non-limitative example has been described below and is illustrated inthe attached drawing, which shows a unit made of two columns for theproduction of gaseous oxygen under pressure.

The atmospheric air to be separated is compressed in a blower 1 at anabsolute pressure of about 8.5 kg./cm. and cooled in a water-cooler 2.It leaves the cooler at about 27 C. The air is then divided into twofractions. The first one (about 77.5% of the total of air treated)enters regenerator 4A through pipe 3 and loses its moisture and itscarbon dioxide. The purified air leaves the regenerator at a temperaturewhich is slightly higher than its dew point and, through pipe 6, entersthe high pressure rectification column 18 at an absolute pressure ofabout 8.3 kg./cm. The second air fraction, about 22.5% of the totalamount, is fed through pipe 7 to a compressor 8, where it is furthercompressed to a pressure high enough to allow the vaporization of thecompressed liquid oxygen. If, for example, it is desired to produceoxygen under an absolute pressure of about 6.3 kg./cm. the air iscompressed in the compressor 8 at an absolute pressure of about 21kg./cm.

Through pipe 9, the air is fed to the water-cooler 10. It then entersthe decarbonation tower 11, where carbon dioxide is removed throughcaustic soda scrubbing. The air is then dried in the desiccation unit 12and sent through pipe 12A to the exchanger 13, then to the liquefier 14,in which the air is cooled down and liquefied by indirect heat exchangewith the liquid-oxygen under pressure.

aaiaeoa Through pipe 15, the liquefied air enters coil 16, which isplaced in the lower section of the high pressure column 18. In thiscoil, the high pressure liquid air is further cooled by indirect heatexchange with the liquid boiling in the lower part of this column. Theliquid air is then expanded to an absolute pressure of 8.4 kg/cm.through valve 17, and sent to column 18. This column separates the airinto two fractions: a liquid rich in oxygen, and liquid-nitrogen. Theliquid rich in oxygen leaves the lower part of this column through pipe19 and is then cooled down in exchanger 20. It is then filtered in absorption filter 21, in order to remove acetylene, and sent through valve22 to the low pressure column 23. The high pressure column produces asecond fraction which is liquid-nitrogen. This liquid-nitrogen leavescolumn 18 through pipe 24, is cooled in heat exchanger 25 and sentthrough valve 26 to the top of the low pressure column 23.

The low pressure column 23 works under an absolute pressure of about 2.1kg./cm. It gives two products:

(a) Liquid-oxygen, which is later compressed to an absolute pressure of6.3 kg./cm. through pump 27 and sent through pipe 27A to the exchangers14 and 13, where it is heated, vaporized and finally reheated in thegaseous state, before leaving the unit approximately at ambienttemperature.

(b) Gaseous nitrogen, which leaves the top of column 23, is reheated inheat exchanger 25, expanded to an absolute pressure of about 1.25 lg./c1n. in expansion turbine 28. It is then reheated in heat exchanger20, before entering regenerator 48 through conduit 29. The nitrogenleaves the unit through pipe 30 at approximately ambient temperature andpressure.

I claim:

1. In a process of production of oxygen under pressure by theliquefaction and rectification of air in at least two rectifying zonesunder successively lower pressures, wherein the air to be separated isdivided into two fractions, the first one of which is compressed to ahigher pressure than the second one and cooled by heat exchange withliquid oxygen under pressure, then introduced into a rectifying zone andthe second one of which is introduced under its original pressure into arectifying zone, the improvement of maintaining a higher thanatmospheric pressure in the rectifying zone under the lowest pressure,and expanding with external work the whole of the separated nitrogenfrom said lowest pressure to nearly atmospheric pressure.

2. A process according to claim 1, wherein the nitrogen is reheatedbefore its expansion by heat exchange with a liquid leaving arectification zone and sent to a lower pres! sure rectification zone.

3. A process according to claim 1, wherein the expanded nitrogen isreheated by heat exchange with a liquid originating from a rectificationzone and sent to a lower pressure rectification zone.

4, A process of production of oxygen under pressure by the liquefactionand rectification of air in two rectification zones under successivelylower pressures, comprising, compressing the air to be. separated,dividing it into two fractions, further compressing a first fraction ofthe air, cooling said fraction byheat exchange with liquid oxygen underpressure, introducing it into at least a rectification zone, cooling asecond fraction of the air by heat exchange with cold gaseous nitrogenand introducing it under its original pressure into a rectificationzone, compressing liquid oxygen issued from the lower pressurerectification zone and reheating it by heat exchange with said firstfraction of the air, and expanding with external work the.

whole of the gaseous nitrogen issued from the lower pressurerectification zone and. reheating it by heat exchange with said secondfraction of the air. t

5. A process according to claim 4, wherein the first fraction of the,air is introduced into the higher pressure column.

6. A process according to claim 5, wherein the gaseous nitrogen isreheated before its expansion with external work by heat exchange withliquid nitrogen extracted in the high pressure rectification zone andsent to the lower.

pressure rectification zone.

7. A process according to claim 5, wherein the gaseous nitrogen isreheated after its expansion with external work,

by heat exchange with a liquid enriched with oxygen originating from thehigher pressure rectification zone and sent to the. lower pressurerectification zone.

References Cited in the file of this patent UNITED STATES PATENTS2,496,380 Crawford Feb. 7, 1950 2,499,043 Voorhees Feb. 28, 19502,627,731 Benedict Feb. 10, 1953 2,699,047 Karwat Jan. 11, 19552,763,138 Tsunoda Sept. 18, 1956 2,779,174 Vesque Jan. 29, 19572,827,775 Linde Mar. 25, 1958 2,873,583 Potts Feb. 17, 1959 FOREIGNPATENTS 1,108,033 France Aug. 17, 1955

1. IN A PROCESS OF PRODUCTION OF OXYGEN UNDER PRESSURE BY THE LIQUEFACTION AND RECTIFICATION OF AIR IN AT LEAST TWO RECTIFYING ZONES UNDER SUCCESSIVELY LOWER PRESSURES, WHEREIN THE AIR TO BE SEPARATED IS DIVIDED INTO TWO FRACTIONS, THE FIRST ONE OF WHICH IS COMPRESSED TO A HIGHER PRESSURE THAN THE SECOND ONE AND COOLED BY HEAT EXCHANGE WITH LIQUID OXYGEN UNDER PRESSURE, THEN INTRODUCED INTO A RECTIFYING ZONE AND THE SECOND ONE OF WHICH IS INTRODUCED UNDER ITS ORIGINAL PRESSURE INTO A RECTIFYING ZONE, THE IMPROVEMENT OF MAINTAINING A HIGHER THAN ATMOSPHERIC PRESSURE IN THE RECTIFYING ZONE UNDER THE LOWEST PRESSURE, AND EXPANDING WITH EXTERNAL WORK THE WHOLE OF THE SEPARATED NITROGEN FROM SAID LOWEST PRESSURE TO NEARLY ATMOSPHERIC PRESSURE. 